Unsaturated polyester resins, and particularly reinforced unsaturated polyester resins have wide commercial utility in manufacturing such items as automotive parts, boat hulls, bath and kitchen fixtures (e.g., sink basins, vanity tops, shower units, etc.), aerospace parts, storage tanks and the like. Various fabrication techniques can be used, including among others, hand lay-up, matched metal-die molding, compression molding including the use of sheet molding compound ("SMC") and bulk molding compound ("BMC"), transfer molding, injection molding, and resin transfer molding ("RTM"). Unsaturated polyester resins often have to be cured at elevated temperatures (e.g., temperatures greater than about 40.degree. C. and often greater than about 120.degree. C.) to gain the desired properties, and particularly the desired surface properties. Exposure to elevated temperatures, however, is often detrimental to the quality of the resulting molded article. Moreover, expensive tooling made from heat resistant materials (e.g., steel and chrome) and having means for providing heat to the tool often have to be utilized.
Molding at elevated temperatures is usually required when attempting to mold articles (e.g., automotive exterior parts) that require a smooth surface quality, known as Class A surfaces, and exhibit reduced shrinkage and warpage. When molding Class A articles, compression molding techniques are conventionally used in conjunction with a low profile additive added to the resin. See, for example, U.S. Pat. Nos. 4,525,498 to Atkins et al., 4,172,059 to Atkins et al., and 3,701,748 to Kroekel.
Despite the general availability of unsaturated polyester resins using such additives, there continues to be a need for improvements in molding resins, and particularly molding unsaturated polyester resins at room temperature. Resins that cure (mold) at room temperature have heretofore not been entirely successful when used in molding Class A articles. Conventional thinking is that elevated molding temperatures (e.g., on the order of 120.degree. C. to 160.degree. C.) are necessary to obtain Class A surfaces.